Packet data users are continuously connected to the network typically with only occasional periods of activity. In a continuously connected mode, the users do not relinquish their data channels during periods of inactivity only to re-establish them when traffic is available: this can create delays that would ruin the user experience. In order to allow for a large number of such users, the UEs can be configured to discontinue their DPCCH (continuous dedicated physical control channel) transmissions (i.e., using gating) when not sending data. Users can, for example, transmit one 2 ms TTI (transmission timing interval) of data every 2-5 frames and nothing in between (i.e., no DPCCH during the transmission gaps).
In an uplink (a direction from a user equipment to a network), when no dedicated channels (DCHs) and no corresponding dedicated physical data channels (DPDCHs) are configured, all data is transmitted on an enhanced dedicated channel (E-DCH) which is mapped to an enhanced dedicated physical data channel (E-DPDCH). Control signaling associated with the E-DCH is transmitted on an enhanced dedicated physical control channel (E-DPCCH). The E-DPDCH and E-DPCCH can be discontinuous and are transmitted only when there is data to be transmitted and the transmission has been granted by the network. In the uplink, in addition to the E-DPDCH and E-DPCCH, a continuous dedicated physical control channel (DPCCH) and possibly a continuous or discontinuous dedicated physical control channel (e.g., an uplink high speed dedicated physical control channel, HS-DPCCH) for an HS-DSCH (high speed downlink shared channel) are transmitted.
A packet service session contains one or several packet calls depending on the application as described in ETSI standard, TR 101 112, UMTS 30.03 “Selection procedures for the choice of radio transmission technologies of the UMTS”, version 3.2.0. The packet service session can be considered as an NRT (non-real time) radio access bearer duration and the packet call as an active period of packet data transmission. During the packet call several packets may be generated, which means that the packet call constitutes a bursty sequence of packets. The burstiness is a characteristic feature of the packet transmission. A typical behavior of the packet data traffic is illustrated in FIG. 1.
The UL DPCCH carries control information generated at layer 1 (physical layer). The layer 1 control information consists of, e.g., known pilot bits to support channel estimation for coherent detection, transmit power control (TPC) for DL DPCH (dedicated physical channel), optional feedback information (FBI) and optional transport format combination indicator (TFCI). Typically, the UL DPCCH is continuously transmitted (even if there is no data to be transmitted for certain time periods), and there is one UL DPCCH for each radio link. The continuous transmission is not a problem with circuit switched services, which are typically sent continuously. However, for bursty packet services, continuous DPCCH transmission causes a significant overhead.
The uplink capacity can be increased by decreasing a control overhead. One possibility for decreasing the control overhead is UL DPCCH gating (or discontinuous transmission), i.e., not transmitting signals on the DPCCH all the time.
Rationale for using gating includes (but is not limited to):                providing user equipment (UE) power savings and longer battery life;        providing interference reduction; and        providing higher capacity.        
There is a fast closed loop power control for all uplink signals to combat against the power imbalance between different user signals and fast fading. The Node B, e.g., estimates continuously a signal-to-interference ratio (SIR) of the DPCCH transmitted by the UE and compares an estimate to a target value, and transmits transmit power control (TPC) commands in a downlink to the UE to increase or decrease the transmit power level. With the power control, the signals from different UEs can be received with the required quality in changing conditions.
During the uplink transmission gap the UL power control cannot operate as normally because Node B cannot estimate the received signal quality to determine the proper TPC command (the SIR would be extremely low, and normally generated TPC commands would tell the UE to increase the UL transmit power). Therefore the transmission power to be used after the gap needs to be estimated or predefined. Due to a user movement or a change in propagation conditions (fading) it is likely that in case of a long transmission gap that the power used prior to the transmission gap is not sufficient to ensure a proper communication leading to increased usage of the HARQ (hybrid automatic repeat request) or too excessive thus increasing a UL noise making the UL power control and scheduling of UL capacity (e.g., in case of a high speed uplink packet access, HSUPA) more difficult.
In order to improve radio link performance, a DPCCH preamble with a duration of a few slots can be attached to the transmissions. This has a dual benefit of allowing both power control and channel estimation to adapt to the present link conditions. In terms of HARQ (hybrid automatic repeat request), the preamble can be attached either to the first transmission only, or to the first transmission and to subsequent retransmissions.